As the electronic industry advances rapidly towards manufacturing smaller, lighter, faster, and cheaper products, area array packages including Ball-Grid Array (“BGA”) packages, Chip-Scale Packages (“CSP”), flip chips, wafer bumping and wafer-level packaging (“WLP”) are increasingly becoming the focus of IC packaging technology. Area array packages help to improve device performance and manufacturability, and ultimately reduce manufacturing costs.
However, the reduced dimensions of the devices also lead to more stringent requirements on process control and quality assurance. A particular challenge relates to the development of vision techniques for three-dimensionally inspecting the surfaces of these smaller devices accurately and efficiently. An example would be the inspection of wafer bumps formed on BGA devices.
Specifically, wafer bump heights should be measured and examined in three dimensions to determine if they are defective. However, the small size of the wafer bumps, which typically have diameters of about 60 microns, mean that traditional inspection technologies, such as techniques for inspecting solder bumps on printed circuit boards, are inapplicable. In addition, the highly specular and textureless nature of these devices lead to many difficulties in inspecting their surfaces.
There have been inspection mechanisms proposed for wafer bumps, such as laser triangulation, confocal microscopy and gray-level pattern projection. However, the laser triangulation method is limited by slow speed and low resolution. Confocal microscopy involves moving parts and has limitations in its operation speed. Gray-level pattern projection has the problems of image brightness saturation and high sensitivity to noise.
Further, in inspection methods using continuous gratings (for example, sinusoidal grating methods), several gray-level intensities are used to determine phase displacement to thereby determine surface profile. For this reason it has intrinsic problems like brightness saturation, multi-reflection, and noise or disturbance to gray-level brightness.
It would be desirable to develop a new three-dimensional reconstruction mechanism that is based upon an imaging system that is fast and efficient, and has less noise over current sinusoidal grating systems.